High speed sampling circuit

ABSTRACT

A light intensity control apparatus for use in an information recording and reading system includes a light source driving device for driving a light source so as to generate a light having the first and higher second light intensity levels. A light intensity detection device is provided and includes a first light intensity detection member for detecting a prescribed intensity level of the light when a light modulation speed is relatively low, and a second light intensity detection member for detecting an average of the intensity of the light when it is relatively high. A detection member selection device is provided so as to select one of the first and second light intensity detection members depending upon a selection instruction so as to use one of the detection outputs. A reference level selection device is provided so as to select one of the first and the second reference levels to be compared with the one of the detection results depending upon the selection instruction. A comparison device may be provided so as to compare the one of detection results with a corresponding one of reference levels. A driving current adjustment device is provided in order to adjust the magnitude of a driving current that drives the light source in accordance with the comparison result.

This application a continuation application of U.S. patent applicationSer. No. 09/994,593, filed Nov. 27, 2001, the entirety of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an information recording apparatus,such as an optical disc drive, that records information in a recordationmedium, such as a CD-R/RW disc, and in particular, to a light intensitycontrol apparatus that controls power of a light generated from a lightsource such as a semiconductor laser.

Recently, an information recording apparatus capable of recordinginformation in a recordation medium, such as a CD-R/RW disc, is inwidespread use. For example, Japanese Patent Application Publication No.7-44885 refers to an information recording apparatus, where the first,third and fourth levels of light intensity (P1, P3, and P4) are set asoptical output levels of a semiconductor laser. In addition, theremaining second intensity level (P2=P1+P4−P3) can be set from the threelower optical intensity levels (P1, P3, and P4) as a peak value of arecordation pulse light because the optical intensity value P3 issmaller than P1, and the following inequality is accordinglyestablished:

P 4<P 2, P 3<P 4<P 2

As a result, an unnecessary signal (i.e., signal higher than P2) can beavoided from being recorded in the recordation medium. Accordingly,unnecessary deterioration of the semiconductor laser can be avoided.

Further, when recording some information in an optical disc, an opticaldisc apparatus as an information recording apparatus generally modulatesa recordation laser beam with a higher recordation power (i.e., a higheroptical output level) than when reading information.

When utilizing a writable optical disc, such as a CD-R (Compact DiscRecordable) disc, having an organic colorant recordation coat on arecordation surface, the semiconductor laser light source alternatelygenerates light beams having light power levels P1 (“read” intensity)and P2 (“write” intensity), where P2 is an optical output light powerlevel higher than P1. As a result, a “pit” is created on a portion ofthe recordation surface when the laser light beam is irradiated at thegenerated light power level P2, and a “space” remains on another portionwhen the other portion is irradiated by the generated light power P1.Further, the P3 level, which is higher than the P2 level, is generallyutilized and a recordation power wave sometimes is formed to includethree different values having P1, P2, and P3 levels. The P3 level ispositioned at a pit top portion so as to make a pit edge sharp.

When a rewritable and phase changeable type recordation medium, such asa CD-RW (Compact Disc Rewritable) disc, is utilized, these three opticaloutput power levels are also used. Specifically, a portion irradiated bya laser beam on a recordation surface portion is generally madeamorphous (non-crystal) when the generated light power P3 and P1 levelsare repeatedly utilized at high speed. In contrast, a crystal portion ismade on the recordation surface when the P2 level is maintained. Thesecrystalline and amorphous portions can correspond to information data.

To control these several modulation intensity levels, a sampling circuitis generally utilized. When the generated light intensity levels P1 andP2 for the CD-R are utilized, the P2 level is sampled and is generallycompared with a prescribed reference value. Then the laser currentcarried through the semiconductor laser light source is controlled basedupon the result of the comparison.

Thus, the generated light power is controlled so that the P2 level canequal a prescribed reference level (i.e., target level). In addition,since the P1 level corresponds to reading power, the magnitude of lasercurrent carried during reading generally is stored for later use.

In the above-described information recording apparatus, when themodulation speed becomes extremely high along with an increase in arecordation speed, the time period of the P2 level becomes extremelyshort. As a result, a high speed sampling circuit is required. However,it generally is difficult to provide such a high speed sampling circuit,or costly if provided. In addition, if a less expensive sampling circuitis utilized, the recordation light power is not precise.

SUMMARY OF THE INVENTION

An object of the present invention is to address and resolve the aboveand other problems and provide a new image processing apparatus. Theabove and other objects are achieved according to the present inventionby providing a novel light intensity control apparatus including a lightsource driving device that drives a light source by the first and secondlight intensity levels, a light intensity detection device that detectsintensity of a light generated from the light source, a comparisondevice that compares the light intensity with the first and secondreference levels, and a driving current adjustment device that adjustsmagnitude of a driving current that drives the light source inaccordance with a result of the comparison.

In another embodiment, the light intensity detection device includes afirst light intensity detection member that detects intensity of thelight generated by the second light power level when an operationalspeed is relatively low, and a second light intensity detection memberthat detects an average of the intensity of the light when anoperational speed is relatively high.

In yet another embodiment, a light intensity detection member selectiondevice is provided so as to select one of the first or second lightintensity detection devices based upon a selection instruction so as toselect one of the detection outputs.

In yet another embodiment, the comparison device includes a referencelevel selection device that selects one of the first and the secondreference levels in accordance with the selection instruction.

In yet another embodiment, the selection instruction indicates a digitalmodulation speed of the light source.

In yet another embodiment, the selection instruction controls thedetection member selection device to select the first light intensitydetection member and the reference level selection device to select thefirst reference level, correspondingly, when the digital modulationspeed is relatively low.

In yet another embodiment, the selection instruction controls thedetection member selection device to select the second light intensitydetection member and the reference level selection device to select thesecond reference level when the digital modulation speed is relativelyhigh, where the high speed is higher than the low speed.

In yet another embodiment, the light source driving device drives alight source by all of the first, second, and third light intensitylevels.

In yet another embodiment, the driving current adjustment device adjuststhe magnitude of the driving current so that the light source generatesa light power intensity level having the second reference level basedupon the result of the comparison when the light source is driven by thesecond light generation level.

In yet another embodiment, the driving current adjustment device adjuststhe magnitude of the driving current in accordance with the performancederived from the first and second generated light levels when the lightbeam is generated at the third light intensity level.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a block chart for illustrating a configuration of oneembodiment of a laser power control circuit provided in an optical discapparatus according to the present invention;

FIG. 2 is a chart for illustrating a variety of signal waves utilizedwhen light generation control is performed for a CD-R by a laser powercontrol circuit illustrated in FIG. 1;

FIG. 3 is a chart for illustrating a variety of signal waves utilizedwhen light generation control is performed for a CD-RW by a laser powercontrol circuit illustrated in FIG. 1;

FIG. 4 is a block chart for illustrating an interior configuration of adriver illustrated in FIG. 1;

FIG. 5 is a chart for illustrating a table included in the driver forshowing a relation between a control logic signal and an input signal;and

FIG. 6 is a graph for illustrating a relation between current of a laserdiode (LD) illustrated in FIG. 1 and recordation power.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the drawings, wherein like reference numerals and marksdesignate identical or corresponding parts throughout several views.FIG. 1 shows an information recording apparatus which may be provided soas to record and reproduce information by condensing a laser beam,generated from a semiconductor laser light source, on a recordation coatformed on an optical disc 20, such as a CD-R or CD-RW. A laser powercontrol circuit may be provided to control recordation power (i.e.,generated light power) of the semiconductor laser light source wheninformation is recorded and reproduced.

One example of a recordation system and its operation performed in thelaser power control circuit by utilizing two different light intensitylevels is now described. A pickup 1 may include: a prism 2, asemiconductor laser light source (LD) 3, and a photo-detector (PD) 4.The LD 3 may produce a laser light beam generated with a prescribedlight generation power in correspondence with a driving current carriedfrom the driver 13. The laser beam may be transmitted to an optical disc20 and to the PD 4 after being reflected through the prism 2. Whenreceiving the laser beam from the prism 2, the PD 4 may perform aphoto-electronic conversion and output a signal in accordance with themagnitude of the laser beam. Thus, PD 4 may function as detecting andmonitoring the value of the generated light power of the laser beam. Thepickup 1 may also include an objective and another optical detectorcapable of receiving a reflected light, or the like. However, each ofsections thereof and conventional sections not directly related to thepresent invention are neither described nor illustrated in the drawings.

An amplifier (Amp) 5 may amplify a generated light power monitor signalindicating the magnitude of generated light power after thephoto-electronic conversion by the PD 4. The generated light powermonitor signal may then be input to both a sample-hold circuit (S/H) 6and a low pass filter (LPF) 7 that is a low band filter device. The S/H6 may sample a generated light power monitor signal when a samplingpulse signal (P2SAMPLE) is generated, and hold the corresponding lightintensity level data.

As illustrated in FIG. 2(d), when a CD-R disc is utilized, the samplingpulse signal (P2SAMPLE) may be generated and input to the S/H 6 at aportion of the second light intensity level P2 higher than the P1 thatis a minimum light intensity level enabling the LD 3 to generate a lightbeam for reading. When the CD-RW is utilized, the sampling pulse signal(P2SAMPLE) may be generated at the second light power intensity level P2of the generated light power for erasing (it is referred to as arecordation power level similar to the P2 level for the CD-R).

The second light intensity level P2 may be higher than the generatedlight level P1 for reproduction use. Thus, when a CD-RW disc is utilizedand a high speed modulation is performed between the third lightintensity level P3 higher than the second light intensity level P2 andthe first generated light level P1 as illustrated in FIG. 3, arecordation coat may become amorphous, and accordingly, a recordationmark may be formed. When the second light intensity level P2 istransmitted, it transforms the recordation coat into a crystal, therebyforming an erasing mark in a manner known in the art.

When a CD-R disc is utilized, a recordation mark may be formed on arecordation surface of an optical disc 20 when the second lightintensity level P2 is transmitted to the recordation surface. A spacemay remain on the recordation surface if the first light intensity levelP1 is used when reproducing. In addition, by positioning the third lightintensity level P3 at the top of light intensity level P2, asillustrated in FIG. 2(d), the front edge of the recordation mark may bemade sharp, as known in the art. Thus, the S/H 6 may output a prescribedsignal in accordance with the second light intensity level P2.

The LPF 7 may allow passage of a low band part of the generated lightpower monitor signal. Thus, the LPF 7 may detect an average of generatedlight power output from the PD 4. As illustrated in FIG. 2(d), when theCD-R disc is utilized, since an average (PAVE) of the generated lightpower exists in the vicinity of the dotted line, the output of the LPF 7may also be at such a level. In contrast, as illustrated in FIG. 3(d),when the CD-RW disc is utilized, such an output may be at a level inaccordance with the average (PAVE).

Otherwise, the average (PAVE) can be calculated from the third to firstlight intensity levels (P3, P2, and P1) if an average duty of arecordation mark and a space (i.e., an erase mark) is constant, andtimings of the generation of light power from the third to first lightintensity levels (P3, P2, and P1) (i.e., modulation timing) are known.For example, if each of the levels P3 and P2 is 10 mW, the level P1 is 1mW, and the average duty is 50%, the average can be calculated as:

PAVE=(10×0.5)+(1×0.5)=5.5 mW

Thus, the above-described PD 4, Amp 5, S/H 6, LPF 7, and first selector(SEL) 8 may constitute the generated light power detection deviceaccording to the present invention. The S/H 6 may serve as a detectionmember for detecting a value of the first generated light power. The LPF7 may serve as a detection member for detecting the second generatedlight power. In addition, the first SEL 8 may serve as a detectionmember selecting device.

The first SEL 8 may select any one of outputs from the S/H 6 and the LPF7 depending upon a selection instruction (i.e., selection of High Speed:HS). In particular, if the digital modulation speed of the LD 3, andaccordingly, a speed of recordation in the optical disc 20 is relativelylow, the selection instruction HS may be zero (HS=0). Then, the firstselector 8 may select and output an output signal from the S/H 6 to thecomparison circuit 9.

In contrast, if the digital modulation speed, and accordingly, therecordation speed are relatively high, the selection instruction HS maybe one (HS=1). The first selector 8 may select and output an outputsignal from the LPF 7 to the comparison circuit 9. Thus, when anoperation is performed at high speed, instead of using the S/H 6, amonitor signal that indicates an average power obtained by the LPF 7 maybe utilized. Then, the comparison circuit 9 may compare a generatedlight power monitor signal that is output from the first selector 8 witha reference level (P2REF) that is output from a second SEL 11. Thecomparison circuit 9 may then output a signal that indicates the resultsof the comparison. The reference level (P2REF) may be a target levelthat the generated light power monitor signal reaches so as to controlthe generated light power of the LD 3.

Thus, the comparison circuit 9 and the second SEL 11 may constitute thecomparison device according to the present invention. The second SEL 11may serve as the reference level selection device. In addition, thesecond SEL 11 may select and output to the comparison circuit any one ofthe first reference level RefL and the second reference level RefH as areference level (P2REF) depending upon the selection instruction (HS).

Specifically, the second SEL 11 may select and output to the comparisoncircuit 9 the first reference level RefL if the selection instruction HSindicates a low speed (i.e., HS=0). In contrast, the second SEL 11 mayselect and output to the comparison circuit 9 the second reference levelRefH if the selection instruction HS indicates a high speed (i.e.,HS=1).

Since the first reference level RefL is selected when the sample holdvalue of the second light intensity level P2 is selected as a generatedlight power monitor signal, a prescribed level, corresponding to thesecond light intensity level P2, may be set to RefL. Since the secondreference level RefH is selected when an average value is selected as agenerated light power monitor signal, a prescribed level, correspondingto the average intensity level, may be set to the RefH.

The amplification circuit 10 may amplify the comparison resultindication signal that is output from the comparison circuit 9. A signalIP2 (described later in detail) may be output from the amplificationcircuit 10 and then input to the driver 13. When a recordation pulse WD2is formed from write data (WDATA) and input as high level (“H”) then thedriver 13 may carry a driving current having magnitude in proportion tothe output signal IP2 through to the LD 3. When the pulse WD2 is a lowlevel (“L”) then the driver 13 may carry a driving current havingmagnitude in proportion to the level of the input signal IP1 through tothe LD 3.

Thus, generated light power of the LD 3 can be adjusted. Accordingly,the driver 13 may serve as the light source driving device and drivingcurrent adjusting device according to the present invention.

Further, the above-noted selection instruction may control the generatedlight detection member selection device to select the first generatedlight power detection member and the reference level selection device toselect the first light reference level (i.e., RefL) when a digitalmodulation speed of the light source is relatively low. Moreover, it maycontrol the second generated light detection member selecting device toselect the power level detection device and the referencelevel-selecting device to select the second light reference level when adigital modulation speed of the light source is relatively high.

In the above-described laser power control circuit, for a level of theinput signal IP1, an appropriate laser current may preferably be storedduring reproduction (i.e., the LD 3 is generating a light beam at thefirst light intensity level P1) and then given when recordation isperformed. A conventional control device, not illustrated in drawings,may be provided to control reproduction power to be constant at thefirst light intensity level P1. For example, a generated light powermonitor signal of the first light intensity level P1 may be comparedwith the reference level and then amplified. The generated light powermonitor signal may then be given to the driver 13 as input signal IP1.Such an input signal IP1 may preferably be stored in an appropriatememory. For example, the input signal IP1 can be stored by digitizing itto an A/D converter, holding it in a latch circuit, and then convertingit back into analog by the D/A converter using known techniques in theart.

Another example of a recordation control operation performed in thislaser power control circuit using three different light intensity levelsis now described. The interior configuration of the driver 13 of thisexample may be illustrated in FIG. 4. Specifically, the first to thirdcurrent sources 22, 23, and 24, may be provided to respectively generatea driving current having a proportional magnitude to each level of thecontrol-input signals, IP1, IP2, and IP3. The first to third switches25, 26 and 27, may be opened and closed by control logic signals SW1,SW2, and SW3 generated by the logic section 21 in accordance with thecombinations of input signals WD1 and WD2. The logic section 21 may beconfigured to switch over and carry a driving current to the LD 3 sothat the LD 3 can generate a laser beam having prescribed magnitude ofgenerated light power corresponding to the first to third lightintensity levels P1 to P3 based upon the input signals WD1 and WD2.

FIG. 5 provides an example table showing the relationship between thedifferent statuses of the control logic signals SW1 to SW3 and inputsignals WD1 and WD2. When both of input signals WD1 and WD2 are both lowstates (“L”), the control logic signal switch SW1 may be turned ON and adriving current having magnitude corresponding to the control inputsignal IP1 (i.e., the first light intensity level P1) may be carried tothe LD 3. When the input signals WD1 and WD2 are high state (“H”) andlow state, respectively, the control logic signal switch SW3 may beturned ON and a driving current having magnitude corresponding to thecontrol input signal IP3 (i.e., the third light intensity level P3) maybe carried to the LD 3. When the input signals WD1 and WD2 are in thestate of “L” and “H”, respectively, the control logic signal switch SW2may be turned ON and a driving current having magnitude corresponding tothe control input signal IP2 (the second light intensity level P2) maybe carried to the LD 3.

Even though the driver 13 carries the driving current corresponding tothe first to third light intensity levels, P1 to P3, in theabove-described embodiment, an operation using only the first and secondlight intensity levels P1 and P2 (i.e., two) may be sufficient if asufficient recordation performance of the recordation coat can beattained. For example, two levels of light intensity may be enough for arecordation coat of a certain type of an organic colorant—such as a CD-Rdisc. Since three levels are generally required for a phase changerecordation coat, such as a CD-RW disc, the three levels of lightintensity may be appropriate. When only the two levels are utilized, itis desirable that the input signal WD1 is maintained at a low level(“L”), and a signal substantially the same as the recordation data WDATAis input for the input signal WD2.

Even though the above-described embodiments exemplify a situation whereany one of the control logic signal switches SW1 to SW3 is turned ON,the driving current, having magnitude corresponding to any one of thefirst to third control input signals IP1 to IP3, is carried to the LD 3,the present invention is not limited to those examples and a belowdescribed current accumulation type may be employable. Specifically, forthe first light intensity level P1 (corresponding to the control inputsignal IP1) the first control logic signal switch SW1 may be turned ON.For the second light intensity level P2 (corresponding to the sum of thecontrol input signals IP1 and IP2) the first and second control logicsignal switches SW1 and SW2 may simultaneously be turned ON. Further,for the third light intensity level P3 (corresponding to the sum of thecontrol input signal IP1, IP2, and IP3), the first, second and thirdcontrol logic signal switches SW1, SW2, and SW3 may simultaneously beturned ON.

Such a current accumulation type may readily be realized if its logic isformed from combinations of the timing of the input signal WD1 and WD2is appropriately changed in accordance with power level generationtiming.

One example of a desirable operation using two level generated lightpowers (i.e., the first and second light intensity levels P1 and P2) isnow described. Initially, the driver 13 may hold a light intensity levelcorresponding to a driving current carried when the LD 3 is controlledat reproduction power as a control-input signal IP1. Then, the selectioninstruction HS may be zero (HS=0) when the recordation speed isrelatively low. Otherwise, the selection instruction HS may be one(HS=1) when the recordation speed is relatively high. In addition, theinput signal WD1 may be maintained at a low level (“L”) (for the reasonsnoted earlier). Furthermore, a signal substantially the same as therecordation data pulse WDATA may be input to the driver 13 as an inputsignal WD2. Then, as described above, a sample value of the second lightintensity level P2 or an average value may be selected by the selectioninstruction HS as a generated light power monitor signal.Simultaneously, the reference level (P2REF) may correspondingly beselected as a target power level. Thus, the second light intensity levelP2 of the LD 3 can be controlled at a point around a prescribed targetlevel when a recordation speed is either high or low without employing ahigh speed sampling circuit.

Another example of a generated light power control operation performedby the third light intensity level P3 is now described. The third lightintensity level P3 may be calculated using a laser performance (ratio ofpower to current). Such a laser performance may be calculated from alevel corresponding to the magnitude of a driving current for generatingthe second light intensity level P2.

One example of a method for calculating the laser performance in theperformance calculation section 12 is now described. It is initiallysupposed that the driver 13 is a current switching type as illustratedin FIG. 4. The laser performance can be determined from the controlinput signal IP2 when the LD 3 generates a light beam, having the secondlight intensity level P2, and a control input signal IP1, required whenthe LD 3 generates a light beam having the first light intensity levelP1, by employing the following formula:

Performance=(P 2−P 1)/(IP 2−IP 1)

As illustrated in FIG. 6, the laser performance may be represented byinclination of a straight line. Thus, a control-input signal IP3required for the LD 3 to generate a light beam having the third lightintensity level P3 may be obtained from the following formula:

IP 3=IP 1+(P 3−P 1)/Performance

As for the control input signal IP2 required for the LD 3 duringgeneration of a light beam at the second light intensity level P2, it isdesirable to set the selection instruction to zero (HS=0) and utilize acontrol input signal IP2 as utilized when the second light intensitylevel P2 is controlled by sampling. If the laser performance value isonce obtained, since a control input signal IP3 corresponding to anoptional third light intensity level P3 can be calculated, no problemoccurs even when the selection instruction HS is set to one.

In the above-described laser power control circuit of FIG. 1, thevoltage current of the reference level (P2REF) is used as the secondlight intensity level P2 when the performance calculation section 12calculates the performance. However, the addition of another light levelintensity level does not create any problems if it simply corresponds tothe second light intensity level P2. Specifically, it is sufficient onlyto convert a scale between the laser performance and the third lightintensity level IP3 when a calculation is performed. It is enough tocalculate by converting the first and third light intensity levels, P1and P3, into substantially the same unit as the reference level (P2REF).

Furthermore, the laser power control circuit of the above-describedembodiment can be applied to another system as a device capable ofadjusting a driving current and controlling generated light power of alight source.

Furthermore, even though the illustrated driving current is adjusted bytwo or three values of light intensity levels, the present invention isnot limited thereto. Specifically, the drive current may be adjusted tofour or more different light intensity levels in the similar manner.

According to these embodiments, since the driving current of the lightsource is adjusted by switching a sampling monitor to and from anaveraged monitor, depending upon a recordation speed, high-speedmodulation is available without using a high speed sampling circuit. Inaddition, a light source control to generate a light beam havingprescribed power (i.e., recordation intensity) can be preciselyperformed in either low speed or high speed recordation. Furthermore,since the generated light power is adjusted by the three light intensitylevels, the present invention can be applied to a variety of opticalinstruments, or the like, as a generated light power control apparatus.

The mechanisms and processes set forth in the present invention may beimplemented using one or more conventional general purposemicroprocessors and/or signal processors programmed according to theteachings in the present specification, as will be appreciated by thoseskilled in the relevant arts. Appropriate software coding can readily beprepared by skilled programmers based on the teachings of the presentdisclosure, as will also be apparent to those skilled in the relevantarts. However, as will be readily apparent to those skilled in the art,the present invention also may be implemented by the preparation ofapplication-specific integrated circuits by interconnecting anappropriate network of conventional component circuits, or by acombination thereof, with one or more conventional general purposemicroprocessors and/or signal processors programmed accordingly. Thepresent invention also includes a computer-based product, which may behosted on a storage medium and include, but is not limited to, any typeof disk including floppy disks, optical disks, CD-ROMs, magnet-opticaldisks, ROMs, RAMs, EPROMs, EEPROMs, flash memory, magnetic or opticalcards, or any type of media suitable for storing electronicinstructions.

Numerous additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeunderstood that within the scope of the claims, the present inventionmay be practiced beyond that which is specifically described herein.

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2000-362713, filed on Nov. 29, 2000, the entire contentsof which are incorporated herein by reference.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A light intensity control apparatus,comprising: a light source driving device configured to drive a lightsource to generate a light having at least first and a second lightintensity level, said second level being higher than the first level; afirst light intensity detection device configured to detect the secondlight intensity level and provide an output; a second light intensitydetection device configured to detect an average of the intensity of thelight and provide an output; a light intensity detection deviceselection device configured to select one of the first and second lightintensity detection devices in accordance with a selection instruction;a reference output device configured to output one of a first and secondreferences of a second light intensity level and an average lightintensity level corresponding to the selection instruction; a comparisondevice configured to compare one of the outputs of the first and secondlight intensity detection devices with the corresponding outputted oneof the first and second references; and a driving current adjustmentdevice configured to adjust a magnitude of a driving current configuredto drive the light source in accordance with the comparison result.
 2. Alight intensity control apparatus comprising: a light source drivingdevice configured to drive a light source to generate a light having atleast a first, second, and third intensity levels, said second levelbeing higher than the first level, said third level being higher thanthe second level; a first light intensity detection device detectiondevice configured to detect the second light intensity level and providean output; a second light intensity detection device configured todetect the second light intensity level and provide an output; a lightintensity detection device selection device configured to select one ofthe first and second light intensity detection devices in accordancewith a selection instruction; a reference output device configured tooutput one of a first and second references of a second light intensitylevel and an average light intensity level corresponding to theselection instruction; a comparison device configured to compare one ofthe outputs of the first and second light intensity detection deviceswith the corresponding outputted one of the first and second references;and a driving current adjustment device configured to adjust a magnitudeof a driving current configured to drive the light source in accordancewith the comparison result.
 3. The light intensity control apparatusaccording to claim 2, wherein said third light intensity level isgenerated by determining a performance of the light source referring tothe first and second generated light levels.